1. Field of the Invention
The present invention relates to internal combustion engines, and specifically to fuel injectors for small internal combustion engines.
2. Description of the Related Art
Internal combustion engines have at least one combustion chamber defined therein, each chamber having a spark plug associated therewith. Fuel enters the combustion chamber and is ignited by the spark plug to operate the engine. One method of moving fuel into the combustion chamber is to use fuel injectors which inject a regulated amount of fuel into the chamber to be ignited.
There are several types of fuel injectors used to deliver fuel to the engine""s combustion chambers. One type of commonly used fuel injector is a port type fuel injector. Port type fuel injectors are generally classified as one of two types including spray nozzles where the fuel flow is controlled at the fuel pump by fuel pressure, and spray nozzles including a control device such as a solenoid to control the duration of the spray action. Another type of fuel injector is a direct type fuel injector which provides injection of fuel directly into the compression chamber. This type of fuel injector has two actuators, one for controlling a metering rod or needle, and one for controlling the volume and pressure of a fuel chamber defined in the injector adjacent the discharge orifice.
Although fuel injectors have become an increasingly common component of internal combustion engines, particularly those used in automobiles, the actuation of fuel injectors used in small engines can be problematic. Previous actuation methods for fuel injectors have included the use of solenoids to control the injection of the fuel into the combustion chamber. However, such solenoids generally allow for only a single injection rate of fuel, and thus would be unable to adjust the amount of fuel being injected to correspond to different applications or environments of the engine.
Other actuation methods have included the use of certain piezoelectric devices. In U.S. Pat. No. 6,435,430 (Ruehle et al.), the piezoelectric actuator is used to actuate a fuel injector. The actuator is mounted to a base plate to which a needle is attached. As the actuator expands, the base plate is forced upwardly thus causing the needle to unseat from the discharge port. A compression spring is located between the base plate and fuel inlet connection piece of the fuel injector housing to return the needle to its seated position. Although Ruehle et al. uses a piezoelectric actuator to operate the fuel injector, the assembly of the fuel injector is complicated requiring several components. Further, a spring is required to return the needle to its closed position.
A fuel injector which would be simple, inexpensive, and accurate for the operating conditions of the engine is desirable.
The present invention relates to fuel injectors for use with small internal combustion engines. A first embodiment provides a port type fuel injector having a metering rod for controlling the flow of fuel through a spray orifice in the body of the fuel injector. A piezoelectric actuator is attached directly to the metering rod and the piezoelectric actuator and metering rod assembly is mounted to the fuel injector body by a vented retaining or end cap. When the piezoelectric actuator is distorted in proportion to an input voltage, the actuator moves the metering needle to open the spray orifice. The input voltage, and subsequently the distortion of the actuator, may be varied in accordance with the readings from a throttle position sensor, or an oxygen sensor, for example.
A second embodiment of the present invention uses piezoelectric actuators in a dual actuator, or direct, type fuel injector. The direct type fuel injector has a injector body in communication with the combustion chamber and which receives low pressure fuel into a fuel chamber thereof. A piezoelectric actuator is used to move a piston that defines with the fuel injector body a fuel chamber. The piston is moved by the actuator to close the fuel chamber inlet and pressurize the fuel located in the chamber. A second piezoelectric actuator is directly connected to the metering needle to facilitate movement thereof. The fuel injection is then controlled by both the duration that the inlet port is open and distance the metering needle is lifted from its seat.
One advantage of the fuel injectors of the present invention is that the piezoelectric actuators are mounted directly to the metering needle or piston which allows for accuracy when delivering fuel to the combustion chamber. Further, the piezoelectric actuators are mounted in the fuel injectors by the end caps thereof, simplifying assembly and reducing the cost of the fuel injector.
One form of the present invention provides a fuel injector having a fuel injector body defining a fuel chamber therein. The fuel injector body includes at least one inlet in communication with the fuel chamber and has a retaining cap secured thereto. At least one outlet is defined in the fuel injector body. At least one control member is in the fuel chamber selectively variably engaging the outlet to cause the outlet to be in one of a range of conditions from fully open to fully closed. At least one piezoelectric actuator is directly connected to the control member. The actuator is secured to the injector body by the retaining cap and is distorted when an external voltage is applied thereto. When the actuator is distorted, the control member is moved, selectively changing the condition of the outlet.
In another form of the present invention the fuel injector body includes at least one inlet in communication with the fuel chamber. At least one outlet is defined in the fuel injector body. At least one control member is in the fuel chamber selectively variably engaging the outlet to cause the outlet to be in one of a range of conditions from fully open to fully closed. A piston is mounted in the injector body in surrounding relationship of the control member. A first piezoelectric actuator is directly connected to the control member and a second piezoelectric actuator is directly connected to the piston. The actuator is distorted when an external voltage is applied thereto which moves the control member and selectively changes the condition of the outlet.